The present invention relates to ethernet networks. More specifically, the present invention relates to collision protocols for ethernet networks.
Communication networks such as computer networks are increasingly used in interconnecting a plurality of computers each of which independently executes tasks while communicating information over the network for shared use. The volume of information which may be transferred over such networks has increasingly become more demanding on the structure of the networks themselves. Various network devices are known to allow the connection of a greater number of computers to a single network and further to allow more free communication of information between computers or other devices on the network or on other interconnected networks. As the number of devices on networks increases, the demands for high performance repeaters and other devices to meet the challenge of managing the information flow so that the data does not create a bottleneck effect on the network are increasingly required. Furthermore, the protocol supporting communications over such networks are typically evolving to support higher data rates and larger volumes of information transmittal over the communication networks.
One example of such a communication protocol is known as the ethernet protocol as defined by the Institute of Electrical and Electronic Engineers (IEEE) 802.3 standard. The ethernet protocol is one of the most widely implemented local area network (LAN) standards. An updated version of the ethernet protocol, fast ethernet, is specified to support data transfer rates of 100 megabits per second (Mb/s). A further version, gigabit ethernet, is specified as supporting data rates of 1,000 Mb/s. The developments in the standard related to such technical progress in general have been based on the physical layer, i.e., on the lowest or first layer of an open system interconnection (OSI). While developments and commercialization of faster physical layers has progressed, the protocols for the media access controllers (MAC) currently used in ethernet networks have seen relatively little change.
One problem encountered with ethernet as a result of the increasing performance of personal computers and the number of hosts using a single network, thereby creating increased volumes of traffic on the network, is that difficulties may occur using carrier sense multiple access/collision detection (CSMA/CD) methods such as those provided by ethernet for conventional MAC protocols. A CSMA/CD type host (terminal/computer) generally checks carriers on a transmission path of the network before transmitting frames. The host then transmits a frame during what appears to the host to be an idle period on the transmission path. However, such networks allow collisions to occur when two different connected hosts both attempt to transmit frames on the network at the same time. When the collision is detected, the ethernet protocol provides for collision recovery steps including stopping transmission of any remaining parts of a frame currently being transmitted and initiating retransmission of transmission frames which encounter the collision after some time interval which is typically specified by the collision detection recovery protocol in use on the network.
More particularly, when two transmissions of data collide, collision signals with predetermined bits indicating a collision may be transmitted to each host involved in the transmissions which collided. On receiving the collision signals, the host terminals may retransmit the data. The timing of retransmission is typically controlled using a retransmitting algorithm such as a binary exponential backoff (BEB) algorithm. The BEB algorithm generally specifies xe2x80x9c2xe2x80x9d as a common small constant factor by which the time between making retransmission attempts is increased for each subsequent attempt.
For example, when a host A transmits data on the network and a first collision occurs, a retransmission may be attempted after a single minute. If, during the first retransmission attempt by host A, a second collision occurs, another retransmission is attempted after two minutes. If a third collision occurs at this point, another retransmission is attempted after four minutes and so on.
One problem with this type of BEB algorithm is fairness to competing hosts attempting to access the communication channel. For example, assuming that host A attempts a retransmission after four minutes delay when a third subsequent collision occurs, a separate host, host B may transmit data while host A is delayed waiting a specified time period for a subsequent retransmission attempt. If no collision is encountered by host B during its transmission, it will have transmitted its data prior to host A even though xe2x80x9cfairnessxe2x80x9d would dictate that host A be allowed to transmit data prior to host B as host A sought to transmit such data in advance of the request by host B. In other words, when the BEB algorithm is used, it is possible for a host which attempted to transmit data later than another host to transmit data first. This problem is generally referred to as a capture effect and reduces network performance. The capture effect is generally an intrinsic problem when utilizing the CSMA/CD method and may worsen when the number of hosts in a network is sharply increased or when a larger amount of data is transmitted over a network.
In an attempt to solve this problem various algorithms have been developed as modifications over the BEB algorithm. One such algorithm is the capture avoidance binary exponential backoff (CABEB) algorithm. Another is the binary logarithmic arbitration method (BLAM) algorithm. These algorithms are based on the BEB algorithm and may allow for improved methods for calculating the delay times while still facilitating prevention of collisions. However, the CABEB and BLAM algorithms are still subject to the problem of a lack of fairness in access to the network resource.
In a further aspect of operation of ethernet networks, when signal collisions occur in hubs or repeaters in the network, a collision truncation method which detects collisions and transmits collision signals to a host can be used. This method may reduce the delay time required for collision signals to be transmitted to the respective host so that there is less reduction in the performance of the network. Although this method may improve network performance, the problems of collision and unfairness may still exist.
Accordingly, conventional methods for collision detection and recovery create problems in fairness and may often times result in the reduction of the performance of a network. Furthermore, when the traffic load on a network is sharply increased, the data to be transmitted may surpass a maximum transmission time such that information is not successfully transmitted and is lost. Typically, such problems can only be solved in upper layers of the communication hierarchy which may adversely impact the total performance of the communications over the network.
It is, therefore, an object of the present invention to provide systems and methods for collision control on an ethernet network which may decrease the likelihood of collisions.
It is a further object of the present invention to provide systems and methods for collision control on an ethernet network which may reduce capture effect and provide for improved fairness in access to the network.
In order to provide for the foregoing and other objectives, ethernet collision control systems and methods for an ethernet network are provided which utilize a media access controller (MAC) which inserts a counter code in the inter-frame gap (IFG) between frame units when transmitting data of a data size which exceeds the capacity of a single frame of the ethernet protocol. The counter code provides a clock signal which may be received by other hosts on the network when they monitor the network to determine whether they are able to make transmissions. First, by recognizing the counter code between frames as distinguished from an idle period signal, the hosts seeking to transmit are notified that additional frames are expected in the next time window from the currently transmitting host. In addition, a counter is provided on each host which generates a count value from the received counter code received during inter-frame gaps and generates a retransmission criterion for controlling transmissions based on the received counter code. Accordingly, a counter code may be used to prioritize access to the network based upon the sequence with which additional hosts wishing to transmit data access the network responsive to an internally generated transmission request.
In one embodiment of the present invention, A collision control system for an ethernet network is provided including a media access controller (MAC) circuit that provides data for transmission in frame units. The MAC circuit further includes a code generator that generates a counter code that is transmitted in an inter-frame gap (IFG) between frame units. The counter code is distinct from an idle period code specified by the ethernet network. Also included in the collision control system is a transmitter coupling the MAC circuit to the ethernet network that transmits the frame units and the counter code on the ethernet network.
In another embodiment of the present invention, the collision control system further includes a receiver coupling the MAC circuit to the ethernet network that receives transmissions from the ethernet network including frame units and counter codes transmitted by other collision control systems coupled to the ethernet network. In this embodiment, the MAC circuit further includes a counter for generating a transmission criterion responsive to the received counter codes. The counter code may include a start-period, a clock period. The counter may generate a transmission criterion responsive to the clock period. In one embodiment, the clock period includes a plurality of clock signals and the counter generates a counter value responsive to the plurality of clock signals, the counter value specifying a priority for use as the transmission criterion. In addition, the counter code may further include an end period and the counter may be initialized by the start period and count the plurality of clock signals until the end period is received. The MAC circuit may be configured to use the counter value as a coefficient of a binary exponential backoff (BEB) algorithm to control transmission by the transmitter.
In a further aspect of the present invention, a collision control system for an ethernet network is provided including a receiver coupled to the ethernet network that receives transmissions from the ethernet network including frame units and a counter code transmitted by other collision control systems coupled to the ethernet network and a media access controller (MAC) that receives data in frame units and counter codes from the receiver. The MAC circuit includes a counter for generating a transmission criterion responsive to the received counter code.
In yet another aspect of the present invention, methods are provided for collision control for an ethernet network. Frames of data and a received counter code are received from the ethernet network. The received counter code is received between a first and a second of the frames of data. The received counter code is analyzed to determine a transmission criterion and frames of data are transmitted responsive to the transmission criterion. In one embodiment, transmitting operations include generating a plurality of frames of data for transmission, generating a transmit counter code and transmitting the plurality of frames of data on the ethernet network with the transmit counter code inserted in an inter-frame gap (IFG) between each of the plurality of frames responsive to the transmission criterion.
In one embodiment of the method aspects of the present invention, the received counter code comprise a start period and a clock period including a plurality of clock signals and the analyzing operations include generating a counter value responsive to the plurality of clock signals, the counter value specifying a priority for use as the transmission criterion. The plurality of frames of data may be transmitted at a time determined using the counter value as a coefficient of a binary exponential backoff (BEB) algorithm. In one embodiment, the received counter code further includes an end period and a counter value is generated by initializing the counter responsive to the start period, counting the plurality of clock signals and stopping the counting step and setting the counter value responsive to the end period.